Question

我正在尝试在查询中进行查询

id = mCursor.getInt(mCursor.getColumnIndex(DatabaseHelper.COLUMN_SUBJECT_ID)); S = new Subject(id, getSubjectDescById(id)); Subjects.add(S);

getSubjectDescById（）函数自己打开另一个游标。 mCursor在代码之前打开并在之后关闭。嵌套游标有风险吗？如果是这样，那么什么是我的代码的更好的替代

Answer 1

<强> I have not tested this though but i think,Yes you can use Nested cursors

Scenario ：

Step-1> 打开CURSOR-1
Step-2> 打开CURSOR-2并将该光标用作您想要创建的新光标的指针
Step-3> 关闭CURSOR-2
Step-4> 关闭Cursor-1

试试此示例 ::

private void DemoFunction() throws Exception {
        DatabaseHandler mHelper;
        SQLiteDatabase db = null;
        Cursor mCursor1 = null;
        Cursor mCursor2 = null;
        try {
            mHelper = new DatabaseHandler(getActivity());
            db = mHelper.getReadableDatabase();

            //make query for buffet-type 
            mCursor1 = db.rawQuery("<------My First Query ------>", null);
            if(mCursor1.moveToFirst()){
                do{
                    mCursor2 = db.rawQuery("<------My Second Query ------>", null);
                    if(mCursor2.moveToFirst()){
                    do{


                    }while(mCursor2.moveToNext());
                    Log.d("", "");
                  }
                }while(mCursor1.moveToNext());
                Log.d("", "");
            }
        } catch (Exception e) {
            if(isErr==false){
                errMsg=e.getLocalizedMessage();
                isErr=true;
            }
            throw e;
        }finally{
            if(db!=null){
                if(db.isOpen()) db.close();
            }
            if(mCursor1!=null||mCursor2!=null){
                if(!mCursor2.isClosed())mCursor2.close();
                if(!mCursor1.isClosed())mCursor1.close();
            }
        }
    }

注意： - 确保关闭所有游标

Sqlite我可以使用nester游标吗？

1 个答案: